CAMBRIDGE INTERNATIONAL EXAMINATIONS International General Certificate of Secondary Education
CHEMISTRY 0620/06
Paper 6 Alternative to PracticalMay/June 2003
1 hourCandidates answer on the Question Paper.No additional materials required.
READ THESE INSTRUCTIONS FIRST
Write your name, Centre number and candidate number at the top of this page.Write in dark blue or black pen in the spaces provided on the Question Paper.You may use a pencil for any diagrams, graphs or rough working.Do not use staples, paper clips, highlighters, glue or correction fluid.
Answer all questions.The number of marks is given in brackets [ ] at the end of each question or part question.
Centre Number Candidate Number Name
If you have been given a label, look at thedetails. If any details are incorrect ormissing, please fill in your correct detailsin the space given at the top of this page.
Stick your personal label here, ifprovided.
For Examiner’s Use
1
2
3
4
5
6
TOTAL
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1 Look at the diagrams of common laboratory apparatus.
A
B
C
D
ForExaminer’s
Use
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mortar
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stirrer or stirring rod
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tripod
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bunsen burner
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(a) Complete the empty boxes to identify the pieces of apparatus labelled. [4]
(b) What name is given to the separation method in C?
2 A student carried out an experiment to investigate the speed of the reaction between sodiumthiosulphate and dilute hydrochloric acid.
Na2S2O3 + 2HCl → 2NaCl + S + H2O + SO2
Experiment 1
By using a measuring cylinder, 50 cm3 of sodium thiosulphate solution was poured into a100 cm3 beaker. The beaker was placed on a cross drawn on a piece of paper. 10 cm3 ofhydrochloric acid was added to the beaker and the timer started.
The time was taken until the cross could not be seen. The time was recorded in the table.
beaker
eye
aqueous sodiumthiosulphate
paper with crossmarked on it
10cm3 of hydrochloric acid
[Turn over
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Use
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filtration
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D or describe process - liquid is evaporated to obtain crystals
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Experiments 2, 3, 4 and 5
Experiment 1 was repeated using different volumes of sodium thiosulphate as shown in thetable. All experiments were carried out at 25 °C.
3 A student investigated the redox reaction between potassium iodate(V) and iodide ions. Twoexperiments were carried out.
Experiment 1
A burette was filled up to the 0.0 cm3 mark with the solution A of sodium thiosulphate. Byusing a measuring cylinder, a 10 cm3 sample of the solution B of potassium iodate(V) wasadded into a conical flask. A 10 cm3 sample of dilute sulphuric acid was added to the flaskfollowed by 20 cm3 of aqueous potassium iodide.
Solution A was added slowly to the flask until there was a pale yellow colour in the contentsof the flask. Starch solution was then added into the flask and the colour changed to blue-black. Solution A was added to the flask until the colour just disappeared. Use the burettediagram to record the volume in the table.
Experiment 2
Experiment 1 was repeated using solution C of potassium iodate(V) instead of solution B.
Use the burette diagrams to record the volumes in the table and complete the table.
initial burette reading / cm3
17
16
18
final burette reading / cm3
25
24
26
final burette reading / cm3
17
16
18
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same volume in each beaker
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I00cm
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250cm
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3
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3
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3
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3
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3
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3
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Answer the time will be longer [I] because the depth of liquid is less so the
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reaction time will need to produce more sulphur to obscure the cross
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Table of results
[4]
The reaction of the mixture of potassium iodate(V), sulphuric acid and potassium iodide inthe flask produces iodine. Sodium thiosulphate then reacts with the iodine.
(a) (i) In which Experiment was the greatest volume of aqueous sodium thiosulphateused?
(iv) Predict the volume of solution A which would be needed to react completely ifExperiment 1 was repeated with 20.0 cm3 of the solution of potassium iodate.Explain your prediction.
volume of solution A .................................................................................................
In experiment I more than twice the volume in experiment 2
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Solution B was more than twice the concentration of solution C.
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I7.2 x 2 = 34.4 cm
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3
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3
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using twice the volume of potassium iodate produces twice
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amount of iodine, which in turn will need twice the volume of thiosulphate
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I indicator 2 easier to see 3 makes titration more accurate
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4 A mixture of two solid compounds D and E was analysed. Solid D was a zinc salt which issoluble in water. Solid E was an insoluble metal carbonate. The tests on the mixture andsome of the observations are in the following table.Complete the observations in the table.
ForExaminer’s
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tests observations
(a) About half of the mixture of D and Ewas placed in a test-tube. The mixture was heated green to black
condensation formed
(b) The rest of the mixture of D and Ewas added to distilled water in a boiling tube. The contents of the tube were filtered. The filtrate and the residue were kept for the following tests.
test on residue
(c) The residue was transferred from thefilter paper in to a test-tube. About 3 cm3 of dilute sulphuric acid was added. The gas was tested with limewater. ........................................................................
The solution obtained in (c) was divided into two equal portions.
(d) (i) To the first portion was addedexcess aqueous sodiumhydroxide, a little at a time. pale blue precipitate
(ii) To the second portion wasadded excess aqueousammonia, a little at a time. ........................................................................
(e) The filtrate from (b) was dividedinto three approximately equal portions.
(i) To the first portion were addeddrops of aqueous sodiumhydroxide, a little at a time withshaking. ........................................................................
(iii) To the third portion were addeddrops of dilute hydrochloric acidand aqueous barium chloride. white precipitate
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white precipitate
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dissolves to a colourless solution
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white precipitate
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dissolves to a colourless solution
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D is hydrated (zinc) sulphate
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Copper only
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but Cu
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2+
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2+
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5 An experiment was carried out using the apparatus below.
By using a measuring cylinder, 20 cm3 of hydrogen peroxide was placed in the flask and0.8 g of the catalyst, manganese(IV) oxide was added. The bung was replaced and the gascollected was measured at 1 minute intervals. The results were plotted on the grid(opposite).
(a) (i) Draw a smooth line graph on the grid. [1]
(ii) Which result appears to be inaccurate? Why have you chosen this result?
Not on curve or gas has escaped or misreading of syringe
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0.8g
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Leak, loss of gas
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Volumes lower
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volume of gas / cm3
time /minutes
0
20
40
60
80
100
120
140
160
1 2 3 4 5 6 7 8
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6 Beach sand is a mixture of sand and broken shells (calcium carbonate). Calcium carbonatereacts with dilute hydrochloric acid to form a solution of calcium chloride.
Plan an investigation to find out the percentage of shell material in a given sample of beachsand.
4. Filter to remove sand from solution of calcium chloride
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5. Wash to remove traces of solution
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6. Dry residue (sand)
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7. Weigh sand
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8. % shell = Mass of beach sand - mass of residue x I00%
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Mass of beach sand
Summary of Comments on IGCSE Chemistry Paper 6 June 2003
Page: 2 Q1 You are asked the name of the labelled piece of apparatus not the process Q1 A the container is the mortar and the other part is the pestle Q1 B Not thermometer, if a thermometer is drawn the bulb is shaded black to
indicate that it contains mercury Q1 C remember you are not asked the name of the process - filtration - but the
name of piece of apparatus Q1 D Give full name and do not use words such as 'heat'
Page: 3 Q2 Sulphur, which is insoluble in water, is formed Q2 look at this diagram, it will help you to answer (c)
Page: 4 Q2 (a) The solution goes cloudy, this has to be explained Q2 (c) Once the acid and thiosulphate are mixed the reaction starts and so must
the timing. It is not important which goes in first – water or thiosulphate - but the acid must be last. The volume of thiosulphate varies from experiment to experiment, and is generally larger than volume of acid which is always 10 cm³.
Page: 5
Q2 (d) i All points plotted correctly [3]
-1 for each incorrect point Smooth line [1] label [1]
Q2 (d) i each small square on the x axis is 5s
Page: 6 Q2 (e) In the bigger beaker the surface area will be greater so the depth will be
less Q3 Hint - 0.0 is at top of burette Q3 helps with answer to (b) Q3 You must remember that the scale on a burette reads DOWN so this is
17.2 NOT 18.8 cm³
Page: 7 Q3 this line is important, needed to answer a(iv) Q3 (a) ii Usually in question of this type, volume will be in a simple ratio 2:1 Q3 (a) iii Examiners expect more than simple conclusion Q3 (a) iv the line of text above (a)(i) is relevant to answering this part Q3 (a) iv Do not forget units Q3 (b) When most of the iodine has reacted the colour is a pale yellow but when
starch is added it goes to an intense blue black. The thiosulphate is added until it just goes colourless - all iodine has reacted. Very accurate.
Q3 (b) any two
Q2 (d) i This line is an indicative sketch, not a definitive plot ..
Page: 8
Q4 (a) Both (a) and blue precipitate shows a copper(II) salt
Q4 (d) Both (a) and blue precipitate shows a copper(II) salt
Q4 Reaction of cations must be learned
Page: 9 Q4 (e) you are told that it is a zinc salt. So reaction of cations again Q4 (e) iii This is the test for a sulphate
Page: 10 Q5 See (b) Q5 (a) ii An acceptable answer is that some gas has escaped and this was marked
as correct. However if gas has escaped between 4 - 5 minutes all subsequent readings would be lower. The most probable/best explanation is that the volume of gas in the syringe was not read correctly
Q5 (b) it is the catalyst - alters rate but chemically unchanged
Page: 11 Q5 (a) i you are asked in a(i) to draw a smooth curve
is not a smooth curve
Page: 12 Q6 Sand does not react and remains as a solid Q6 Any six of above
